后记

Question

始终进入 FoodTracker 教程;执行此步骤：“实现自定义控件”

https://developer.apple.com/library/content/referencelibrary/GettingStarted/DevelopiOSAppsSwift/ImplementingACustomControl.html#//apple_ref/doc/uid/TP40015214-CH19-SW1

当执行第一个检查点时，模拟器显示一个红色矩形而不是正方形，如教程中所示;在我得到的调试窗格上：

2018-02-09 11:19:42.130595+0100 FoodTracker[7439:80369] [MC] Lazy loading NSBundle MobileCoreServices.framework  
2018-02-09 11:19:42.131628+0100 FoodTracker[7439:80369] [MC] Loaded MobileCoreServices.framework  
2018-02-09 11:19:42.165143+0100 FoodTracker[7439:80369] [LayoutConstraints] Unable to simultaneously satisfy constraints.  
    Probably at least one of the constraints in the following list is one you don't want.  
    Try this:  
        (1) look at each constraint and try to figure out which you don't expect;  
        (2) find the code that added the unwanted constraint or constraints and fix it.  
(  
    "<NSLayoutConstraint:0x60400028a3c0 UIButton:0x7f8a0bd0e330.width == 44   (active)>",  
    "<NSLayoutConstraint:0x60400028cda0 'UISV-canvas-connection' FoodTracker.RatingControl:0x7f8a0bd08890.leading == UIButton:0x7f8a0bd0e330.leading   (active)>",  
    "<NSLayoutConstraint:0x60400028ce40 'UISV-canvas-connection' H:[UIButton:0x7f8a0bd0e330]-(0)-|   (active, names: '|':FoodTracker.RatingControl:0x7f8a0bd08890 )>",  
    "<NSLayoutConstraint:0x60400028c940 'UIView-Encapsulated-Layout-Width' FoodTracker.RatingControl:0x7f8a0bd08890.width == 200   (active)>"  
)  

Will attempt to recover by breaking constraint  
<NSLayoutConstraint:0x60400028a3c0 UIButton:0x7f8a0bd0e330.width == 44   (active)>  

Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger.  
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful.  
2018-02-09 11:19:42.165949+0100 FoodTracker[7439:80369] [LayoutConstraints] Unable to simultaneously satisfy constraints.  
    Probably at least one of the constraints in the following list is one you don't want.  
    Try this:  
        (1) look at each constraint and try to figure out which you don't expect;  
        (2) find the code that added the unwanted constraint or constraints and fix it.  
(  
    "<NSLayoutConstraint:0x60400028a370 UIButton:0x7f8a0bd0e330.height == 44   (active)>",  
    "<NSLayoutConstraint:0x60400028a320 'UISV-canvas-connection' FoodTracker.RatingControl:0x7f8a0bd08890.top == UIButton:0x7f8a0bd0e330.top   (active)>",  
    "<NSLayoutConstraint:0x60400028cf30 'UISV-canvas-connection' V:[UIButton:0x7f8a0bd0e330]-(0)-|   (active, names: '|':FoodTracker.RatingControl:0x7f8a0bd08890 )>",  
    "<NSLayoutConstraint:0x60400028c990 'UIView-Encapsulated-Layout-Height' FoodTracker.RatingControl:0x7f8a0bd08890.height == 110   (active)>"  
)  

Will attempt to recover by breaking constraint  
<NSLayoutConstraint:0x60400028a370 UIButton:0x7f8a0bd0e330.height == 44   (active)>  

Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger.  
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful.

我认为在编程创建按钮并在此处应用自定义约束时会发生一些变化:(我正在使用Swift和Xcode 9）

// Add constraints  
button.translatesAutoresizingMaskIntoConstraints = false  
button.heightAnchor.constraint(equalToConstant: 44.0).isActive = true  
button.widthAnchor.constraint(equalToConstant: 44.0).isActive = true

欢迎提出解决问题的任何提示。

请注意我正在构建一个自定义控件...我发现谷歌搜索的所有笔记似乎都不适用。

Answer 1

忽略我的前两条评论......

在该教程中，您将自定义ratingControl添加为垂直堆栈视图的已排列子视图。这就是为什么不需要约束的原因。

关键是使类@IBDesignable - 允许Interface Builder和Auto-Layout引擎使用类'内在大小来正确地调整大小/位置/显示它。

（在教程中没有注意到，有点令人惊讶。）

Answer 2

后记

这个问题自己消失了。

继续练习，Xcode IDE在视图设计中强调了一些关键点，我被邀请参加＆＃34;点击图标＆＃34;修理;其中一个问题与冲突的禁区有关。

正如#DonMag所建议的那样，必须将RatingControl类标记为@IBDesignable（稍后将在练习中添加此装饰器）以让Xcode立即查看自定义控件的最终结果。几乎：星星没有出现，并且控件不会自动缩放添加星星到控制属性。直到我关闭，再次打开并重建整个项目几次。

教程（为Swift 3.2编写）和实际Xcode（在Swift 4中打开的默认项目）的差异适用。

我的想法是，Apple必须更新它自己的在线文档，以避免人们放松心情，试图弄清楚为什么事情不会像预期的那样发挥作用。

Answer 3

我有同样的问题。此外，红色方块看起来比教程中显示的要大。为了使红色正方形能够接受大小为44的约束，我必须确保RatingControl位于堆栈视图的内部内部，而不是下方。

我要附加图像以阐明“在堆栈视图内部”的含义。

error reproduced, please note red rectangle outside the stack view hierarchy

error fixed, the red rectangle is inside the stack view hierarchy on the left

Answer 4

发生此问题是因为所有子视图的总宽度不等于StackView的宽度。

使用此计算可以解决问题：

let width = (self.frame.width - self.spacing * CGFloat(starCount-1))/CGFloat(starCount)
let height = self.frame.height

............

for _ in 0..<starCount {
        let button = UIButton()
        button.translatesAutoresizingMaskIntoConstraints = false
        button.backgroundColor = UIColor.red
        button.heightAnchor.constraint(equalToConstant: height).isActive = true
        button.widthAnchor.constraint(equalToConstant: width).isActive = true
        button.addTarget(self, action: #selector(RatingControl.ratingButtonTapped(button:)), for: .touchUpInside)
        addArrangedSubview(button)
    }

iOS 11：“无法同时满足约束”

4 个答案:

后记